The present invention relates to a method for actuating an inverter by means of a space vector pulse width modulation, in particular for actuating an electrical machine, wherein the inverter has a plurality of controllable switches and is configured to provide a multi-phase electrical voltage in the form of a voltage space vector, wherein the controllable switches are actuated in such a manner that different duty cycles of the switches are set and a plurality of successive different switching states of the switches is set up to provide the voltage space vector.
The present invention relates further to a device for actuating an inverter by means of space vector pulse width modulation, in particular for actuating an electrical machine, wherein the inverter has a plurality of controllable switches which are configured to provide a multi-phase electrical voltage in the form of a voltage space vector, said device comprising a control unit which is designed to actuate the controllable switches in such a manner that different duty cycles of the switches are set and the inverter assumes a plurality of successive different switching states of the switches in order to provide the voltage space vector.
The present invention finally relates to a motor vehicle drive train comprising at least one electrical machine for providing driving power, an inverter for actuating the electrical machine and a device for actuating the inverter of the type described above.
Different actuating methods are known in general in the field of three-phase consumers and in particular in the field of three-phase machines. As a result, the method of space vector modulation is now typically preferred for actuating the three-phase consumer. In these actuating methods, a space vector is formed by successively setting eight base voltage space vectors. In order to provide the phase voltage, the base voltage space vectors are switched in a pulse-width modulated manner so that a corresponding actuating voltage is generated.
Due to limited switching times of the controllable switches of the inverter, the adjustable operating range or the maximum phase control factor of the inverter is limited, i.e. the duration of individual switching pulses of the switches is limited to a minimum length of time. In order to increase the adjustable operating range of the inverter or to be able to set individual operating ranges despite the limited switching times of the controllable switches, the German patent application DE 10 2008 040 144 A1 proposes that the duty cycles of the controllable switches within a pulse width modulation period are in each case shortened by the length of the duty cycle of the switch that is switched on for the shortest amount of time. In so doing, one of the controllable switches is not switched on over the entire pulse width modulation period and the duty cycles of the remaining switches are in each case shortened by the length of the duty cycle of the switch that is switched on for the shortest amount of time. This will result in one of two zero voltage switching states being replaced by another zero voltage switching state.
A disadvantage with this method is that a minimally admissible pulse duration of the switches can be undershot for certain switching sequences or for switching sequences of the controllable switches in which the duty cycles of the two controllable switches that are switched on for the shortest amount of time have a similar duration.
The method mentioned above can furthermore lead to a non-symmetrical, in particular thermal, load on the power semiconductors and to a shift in the average neutral point voltage.